Our first major objective is to conduct a detailed ultrastructural study of the nerve fibers in the organ of Corti and vestibular sense organs. The tracts of the afferent and efferent fibers will be followed and their terminals and synapses will be studied by serial sections. The number of nerve endings below the sensory cells will be determined and their fiber population will be counted at Corti's tunnel, habenula perforata and internal auditory canal. Ultrastructural changes in nerve endings, nerve fibers and ganglion cells after nerve section, acoustic trauma, and kanamycin and streptomycin toxicity will be investigated. These studies on normal and pathological specimens provide a basis for development of an artificial device to improve hearing in deaf individuals. Our second major objective is to advance our knowledge on endolymphatic hydrops and Meniere's disease. We will produce hydrops in experimental animals by blockage of the endolymphatic duct, and then we will attempt to find a method to reduce the extent of hydrops or prevent the occurrence of hydrops. Some of the methods to be utilized are creation of fistulas in the saccule, reopening of the blocked duct, and use of drugs and chemicals. This study will provide information useful in the treatment of Meniere's disease. BIBLIOGRAPHIC REFERENCES: Kimura, R.S.: Experimental pathogenesis of hydrops. Arch. Oto-rhino-laryng. 212:263-275, 1976. Kimura, R.S., Ota, C.Y., Schuknecht, H.F., and Takahashi, T.: Electron microscopic cochlear observations in bilateral Meniere's disease. Ann. Otol. Rhinol. Laryng. 85:791-801, 1976.